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Fission is a nuclear reaction or radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei and often other particles. The fission process often produces gamma rays and releases a very large amount of energy, even by the energetic standards of radioactive decay.
After an incident particle has fused with a parent nucleus, if the excitation energy is sufficient, the nucleus breaks into fragments. This is called scission, and occurs at about 10 −20 seconds. The fragments can emit prompt neutrons at between 10 −18 and 10 −15 seconds. At about 10 −11 seconds, the
The event is rated level 7 on the International Nuclear Event Scale by the Japanese government's nuclear safety agency. [78] [79] Other than the Chernobyl disaster, it is the only nuclear accident to be rated at level 7, the highest level on the scale, and caused the most dramatic shift in nuclear policy to date.
The current theoretical model of the atom involves a dense nucleus surrounded by a probabilistic "cloud" of electrons. Atomic theory is the scientific theory that matter is composed of particles called atoms. The definition of the word "atom" has changed over the years in response to scientific discoveries.
The term transmutation dates back to alchemy.Alchemists pursued the philosopher's stone, capable of chrysopoeia – the transformation of base metals into gold. [3] While alchemists often understood chrysopoeia as a metaphor for a mystical or religious process, some practitioners adopted a literal interpretation and tried to make gold through physical experimentation.
It was not until 1919 that Rutherford expanded upon his theory of the "positive electron" with a series of experiments beginning shortly before the end of his time at Manchester. He found that nitrogen, and other light elements, ejected a proton, which he called a "hydrogen atom", when hit with α (alpha) particles. [23]
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Ernest Walton was born in Abbeyside, Dungarvan, County Waterford to a Methodist minister father, Rev John Walton (1874–1936) and Anna Sinton (1874–1906). In those days a general clergyman's family moved once every three years, and this practice carried Ernest and his family, while he was a small child, to Rathkeale, County Limerick (where his mother died) and to County Monaghan.